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Re: [PATCH] ARM: fix bug which lowmem size is limited to 760MB

From Nicolas Pitre <nicolas.pitre@linaro.org>
Newsgroups linux.kernel
Subject Re: [PATCH] ARM: fix bug which lowmem size is limited to 760MB
Date 2015-09-07 17:40 +0200
Message-ID <q66Gu-1eb-33@gated-at.bofh.it> (permalink)
References <q4yQy-7Gl-29@gated-at.bofh.it> <q4A5X-YQ-11@gated-at.bofh.it> <q4NZf-3Zz-11@gated-at.bofh.it> <q635U-4u5-29@gated-at.bofh.it>
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On Mon, 7 Sep 2015, Arnd Bergmann wrote:

> Given how much more common 1GB hardware configurations are compared to 768MB
> configuration, we could however think about adding a VMSPLIT_3G_OPT option
> that x86 has (also VMSPLIT_2_75G on ARCH_TILE), to allow using the entire
> 1GB of lowmem without going all the way to VMSPLIT_2G. That option would
> also let us use the entire 768MB on the machines that 	Yongtaek Lee is
> interested in.

That's easy enough:

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 0d1b717e1e..a63970f211 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1470,6 +1470,8 @@ choice
 
 	config VMSPLIT_3G
 		bool "3G/1G user/kernel split"
+	config VMSPLIT_3G_OPT
+		bool "3G/1G user/kernel split (for full 1G low memory)"
 	config VMSPLIT_2G
 		bool "2G/2G user/kernel split"
 	config VMSPLIT_1G
@@ -1481,6 +1483,7 @@ config PAGE_OFFSET
 	default PHYS_OFFSET if !MMU
 	default 0x40000000 if VMSPLIT_1G
 	default 0x80000000 if VMSPLIT_2G
+	default 0xAF000000 if VMSPLIT_3G_OPT
 	default 0xC0000000
 
 config NR_CPUS


That shifts the risk to user space though.  But if there is a regression 
there, it will manifest itself on all systems and not only with some 
particular hardware.


Nicolas
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[PATCH] ARM: fix bug which VMALLOC_START is lowwer than 0xf0000000 Yongtaek Lee <ytk.lee@samsung.com> - 2015-09-03 04:30 +0200
  [PATCH] ARM: fix bug which lowmem size is limited to 760MB Yongtaek Lee <ytk.lee@samsung.com> - 2015-09-03 07:20 +0200
  Re: [PATCH] ARM: fix bug which VMALLOC_START is lowwer than  0xf0000000 Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-09-03 10:10 +0200
    Re: Re: [PATCH] ARM: fix bug which VMALLOC_START is lowwer than  0xf0000000 Yongtaek Lee <ytk.lee@samsung.com> - 2015-09-03 10:30 +0200
      Re: Re: [PATCH] ARM: fix bug which VMALLOC_START is lowwer than  0xf0000000 Lucas Stach <l.stach@pengutronix.de> - 2015-09-03 10:40 +0200
        Re: Re: Re: [PATCH] ARM: fix bug which VMALLOC_START is lowwer than  0xf0000000 Yongtaek Lee <ytk.lee@samsung.com> - 2015-09-03 10:50 +0200
          Re: Re: Re: [PATCH] ARM: fix bug which VMALLOC_START is lowwer than  0xf0000000 Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-09-03 11:20 +0200
            [PATCH] ARM: fix bug which lowmem size is limited to 760MB Yongtaek Lee <ytk.lee@samsung.com> - 2015-09-03 12:40 +0200
              Re: [PATCH] ARM: fix bug which lowmem size is limited to 760MB Nicolas Pitre <nicolas.pitre@linaro.org> - 2015-09-04 03:30 +0200
                Re: [PATCH] ARM: fix bug which lowmem size is limited to 760MB Arnd Bergmann <arnd@arndb.de> - 2015-09-07 13:50 +0200
                Re: [PATCH] ARM: fix bug which lowmem size is limited to 760MB Nicolas Pitre <nicolas.pitre@linaro.org> - 2015-09-07 17:40 +0200
                Re: [PATCH] ARM: fix bug which lowmem size is limited to 760MB Nicolas Pitre <nicolas.pitre@linaro.org> - 2015-09-07 17:50 +0200
                Re: [PATCH] ARM: fix bug which lowmem size is limited to 760MB Arnd Bergmann <arnd@arndb.de> - 2015-09-07 17:50 +0200
                Re: [PATCH] ARM: fix bug which lowmem size is limited to 760MB Nicolas Pitre <nicolas.pitre@linaro.org> - 2015-09-07 21:50 +0200
                Re: [PATCH] ARM: fix bug which lowmem size is limited to 760MB Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-09-08 02:20 +0200
                Re: [PATCH] ARM: fix bug which lowmem size is limited to 760MB Nicolas Pitre <nicolas.pitre@linaro.org> - 2015-09-08 04:10 +0200
                Re: [PATCH] ARM: fix bug which lowmem size is limited to 760MB Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-09-08 10:10 +0200
                Re: [PATCH] ARM: fix bug which lowmem size is limited to 760MB Nicolas Pitre <nicolas.pitre@linaro.org> - 2015-09-08 17:00 +0200
        Re: Re: [PATCH] ARM: fix bug which VMALLOC_START is lowwer than  0xf0000000 Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-09-03 11:10 +0200

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